Background: Capsinoids (CSN), the novel non-pungent capsaicin analogs have been reported to promote
metabolic health and exercise tolerance. However, the effect of CSN on fat oxidation and changes in skeletal
muscle glycogen levels during post-exercise recovery has not been investigated in humans.
Purpose: We examined the effect of CSN supplementation on energy reliance, glycogen resynthesis and molecular
proteins in the skeletal muscle of young adults during post-exercise recovery.
Methods: In this crossover-designed study, nine healthy adult male volunteers (aged 21.4±0.2 years, BMI
21.9±1.3 kg/m2) completed a 60-min cycling exercise at 70% VO2max. Participants consumed either CSN (12 mg,
single dosage) or placebo capsules with a high-carbohydrate meal (2 g carb/kg bodyweight) immediately after
exercise. Biopsied muscle samples (vastus lateralis), blood, and gaseous samples were obtained during 3h postexercise
Results: We found that oral CSN supplementation right after exercise significantly altered the energy reliance on
fat oxidation during recovery. This was evidenced by lower respiratory exchange ratio (RER) and higher fat oxidation
rate in CSN trial. Despite this, acute CSN dosage does not contribute in enhancing the glycogen replenishment
in skeletal muscle during 3h recovery. We identified no significant differences in postprandial glucose
and insulin area under the curve in both trials. Western blot data showed an increased muscle GLUT4 expression,
but no significant response of p-Akt/Akt ratio with CSN during post-exercise recovery.
Conclusion: Our findings conclude that acute CSN intake could change energy reliance on fat oxidation but is
unable to enhance muscle glycogen resynthesis during post-exercise recovery. Thus, ergogenic properties of CSN
in relevance to muscle glycogen restoration following exercise needs to be further investigated in young adults.